Are there any natural processes that correct or reverse climate change? As in: if the Earth got "too warm" are there natural processes that would make the Earth cooler*? And are those effects* expected to be enough to cancel out any human-caused changes?

My friend brought this up in a climate change discussion awhile back and it's been gnawing on me. Please enlighten me!

* Without killing off all of humanity or making the planet more/mostly/completely uninhabitable.

If you are wondering about negative feedback loops (warming causes some cooling) then it is also relevant to consider the positive feedback loops (warming brings more warming).

One of the main positive feedback loops is the albedo effect. The idea is that every part of the Earth reflects incoming radiation back out into space to some degree, and this contributes to keeping the globe cool. If the light is first absorbed and then emitted by the Earth's surface it tends to get trapped by the atmosphere (by CO2 and other greenhouse gasses) since it has been shifted from the visible spectrum to the infrared.

Different materials have different albedos. They are measured as the amount of radiation reflected compared to the incoming radiation, so the numbers range from 0 to 1 with 1 being perfect reflection. The Earth has an average albedo of 0.3, which means most of the visible light hitting us is absorbed. However, the albedos for ice are 0.5-0.7 and for snow it's 0.8-0.9, crazy high reflection compared to the Earth average.

As global warming/climate change starts to heat up the atmosphere, a lot of the permanent ice near the poles and the permafrost of the far northern latitudes are melting and not reforming. When this ice and snow turn into water or soggy land they stop reflecting all that energy back into space and the Earth starts heating up faster. This melts more ice and snow and you have an unfortunate positive feedback loop, at least until all the snow and ice are melted.

Yeah, they define the scale as 0 = perfect absorption and 1 = perfect reflection. If you want to know more basic albedo info I would just hit up the wikipedia page. I don't have specific sites to point you towards for the climate change aspect but a quick google search would get you started nicely.

Climate change is an incredibly tricky business as there are so many systems that can fluctuate greatly with small changes, and we frankly don't know what a lot of them will do. That is also one of the problems with the science as it is reported to the public, IMO, since with so many aspects it is often hard to report a clear picture of what is going on. It is much easier to find and report on small pieces of the picture that might have dire or awesome consequences, but without examining the entire system at once you lose almost all ability to understand the real effects.

With temperatures rising, the water cycle can speed up (evaporation, condensation, and precipitation). This may result in increased cloud cover, which would deflect more heat, and therefore potentially cause cooling. This is a really simple answer, however, and there are probably many more factors that can cause it to vary.

Also, volcanic eruptions release ash and other particulates that are condensation nuclei (cloud-forming particles). One good example is the Krakatoa eruption in 1883, after which the Earth's average global temperature fell by as much as 1.2 degrees Celsius in the year following (they returned to normal, however, after that).

That's all I can think of at the moment, there may be others. I also don't know if they would be enough to offset anthropogenic effects.

volcanic eruptions also release carbon though, so when the ash eventually settles, the cooling effect is gone while the Earth's atmosphere had a net increase in carbon, leading to further greenhouse effects.

One negative feedback effect would be that with polar regions thawing, they would become more suitable for plant life that would trap atmospheric carbon, though the cooling effect of this would take a very long time to be felt, since it does nothing to actually cool the atmosphere, merely to reduce its greenhouse effect.

Generally it appears that there are more positive feedback effects, such as thawing ices releasing trapped methane, in addition to oceans being able to hold less dissolved carbon dioxide and methane, leading to further greenhouse gasses in the atmosphere, while simultaneously making it more difficult for the oceans to trap them. Not to mention that there hasn't been any decrease in the amount of anthropogenic greenhouse gas emissions worldwide, and no indication that they will stop. Even if stopped completely one day, the planet would still take a long time to reduce the greenhouse effect to pre-industrial levels, all the while continuing to gain heat at rates not seen in pre-industrial times. There aren't very many ways that the planet can lose heat short of some sort of cataclysm that shuts out a good portion of sunlight. Radiation, for a body as large as the Earth, takes a very long time to reduce the average temperature.

Let's think about this for a second, though. Volcanic eruptions are often driven by changes in crustal stress fields. Crustal stress can change as a product of changes in ice-loading. Ice is a climatically sensitive feature of the Earth-climate system.

So if we wished to see whether volcanoes indeed responded to changes in climate, we might look to a large, known source of climatic change that has occurred multiple times over the period for which we have proxy data for volcanic activity.

If we look at evidence of volcanic activity, like ash plumes, in ocean sediment chronologies, and see if they correlate to known orbital forcings, we can see that they appear as a lagged response to obliquity forcing-driven changes in ice volumne/sea level, and thus crustal stress (Kutterolf et al., 2012).

This is not to claim that volcanic eruptions are in fact a feedback, but we should not be too quick to deny any sort of correlation between climatic changes and volcanic activity.

The clouds and albedo comments above are good examples of feedbacks working in opposite directions. From what we know about how these systems work, the positive feedbacks are much stronger than the negative ones (e.g. clouds). Here's a good explanation of the cloud feedback: http://www.skepticalscience.com/clouds-negative-feedback.htm

Also, not a true feedback, per se, but the Earth will absorb back the CO2 through a number of processes (e.g. burial of organic carbon, dissolving into the oceans and precipitated as limestone, etc). However, the timescale of this is on the scale of 10,000's of years. So until then, we are going to have to deal with the impacts of pumping this stuff into our atmosphere.

This is a very good question! Understanding the answer to this actually will give you a much more sophisticated understanding of how climatic change occurs than simply knowing that greenhouse gases prevent longwave radiation from escaping.

As /u/FatSquirrels points out, the question is not whether or not there are any negative feedbacks (there are!), but rather whether the net impact of all feedbacks, both positive and negative, will result in an overall amplification or dampening of a given change in radiative forcing.

Are there any natural processes that correct or reverse climate change? As in: if the Earth got "too warm" are there natural processes that would make the Earth cooler*?

There are indeed negative feedbacks. The primary response of a body like the Earth receiving an increase in radiative forcing is to warm to a higher equilibrium globally-averaged surface temperature. However, it also radiates proportionately more energy out to space, reducing the total amount of energy in the system relative to the full amount of change. The increase in radiation is four times greater than the increase in temperature. This is called the Stefan-Boltzmann response.

Probably the next most important "fast" negative feedback is lapse rate. When there is an increase in radiative forcing, the surface heats up, and this warming propagates upward through the troposphere. The upper troposphere is expected to warm proportionately more than the surface, radiating energy back into space more efficiently, thus reducing the impact of an increase in energy somewhat.

These are the dominant feedbacks that operate relatively quickly. In addition, there are "slow" negative feedbacks that will ultimately scrub carbon out of the atmosphere over tens of thousands of years.

On land, there is weathering. As we increase CO2 in the atmosphere, we will also increase precipitation resulting in more CO2 being removed from the air and hydrolyzed by silicate and carbonate rocks into clays, bicarbonate, and other ions.

Carbon injected into the atmosphere also gets removed by the ocean. In the ocean there are calcifying organisms and their "corpses" which comprise an enormous store of calcium carbonate. As CO2 infiltrates the ocean and increases H+ ions, this calcium reservoir will react and eventually neutralize the increase.

Some people mistakenly believe that plant life will increase as a result of CO2 increases, acting as a negative feedback as the vegetation sucks up CO2 to build more plants. While this may be true in some regions and even globally for an initial increase in CO2, low levels of CO2 are rarely the limiting factor in plant growth in the real world. Other nutrients, temperature, and water are typically the limiting factor on their growth, and the climatic consquences of increasing CO2 will include heat and water stress increases that are expected to balance and then overwhelm the benefits from elevated CO2 levels for global vegetation. So despite "skeptic" claims to the contrary, plants are not expected to be a large negative feedback over the long term, and in fact are expected to contribute to an overall positive carbon cycle feedback (which also includes the inundation of tropical vegetation resulting in methane increases, as well as permafrost thawing and increased soil respiration in high latitude/colder climates).

And are those effects* expected to be enough to cancel out any human-caused changes?

No. We know from the paleoclimatic record that result of a given increase in radiative forcing is greater than the direct response alone, i.e. the net sign of all feedbacks is positive. Paleoclimate data, theoretical/modeling experiments, and observational data indicate that although an increase in radiative forcing of ~3.7W/m2 should increase the globally-averaged surface temperature by ~1.2°C, the actual increase on timescales of thousands of years is closer to 3°C. Positive feedbacks, such as water vapor, ice-albedo, etc. thus appear to more than cancel out negative feedbacks.

The "slow" feedbacks I mentioned will ultimately win out in the end (though much too late for humans to care about). After tens of thousands of years a given increase in carbon will be scrubbed out of the atmosphere and neutralized in the ocean, resulting in a return to essentially pre-increase levels.

Edited to add:

Clouds are not an example of a known, significant negative feedback (though this is a common misconception).

Clouds are indeed a net source of cooling, but that obscures the fact that they both warm and cool, depending on a variety of factors not the least of which is the type and location of cloud. So while clouds will remain a source of cooling as we warm, whether they will be a source of increased cooling (i.e. a negative feedback), less cooling (positive feedback) or neutral is not a simple function of whether there will be fewer or more clouds. If low cloud cover increases proportionately less (or decreases) than high clouds, the net effect will be a positive feedback, not a negative feedback. Again, this is an oversimplification- in reality, there are a host of additional considerations besides changes in altitude, including latitude, storm track shifts, etc.

So far, we have provisional observational evidence that suggests clouds are a moderate positive feedback- though we cannot rule out that they may be a very small negative feedback. But we can rule out that they are such a negative feedback as to overwhelm the strong positive feedback of water vapor.

A large negative cloud feedback is inconsistent with the paleoclimatic record, our theoretical understanding of climate dynamics, and the observations we have so far.